New photographic emulsion with a high degree of covering power

ABSTRACT

Photographic silver halide gelatin emulsions are improved in covering power by pretreatment of a portion of the gelatin colloid binder with an enzyme that hydrolyzes the gelatin. Further improvement is obtained by treating the same portion with organic diacid anhydride, either before or after enzymatic action. Examples describe treatments with trypsin and phthalic anhydride.

United States Patent Claude Guy Doste; Jean Clement Collange; Guy Henri Leverrier, all of Vincennes, France lnventors NEW PHOTOGRAPHIC EMULSION WITH A HIGH DEGREE 0F COVERING POWER 20 Claims, No Drawings U.S. Cl 915/1148 Int. Cl G03c l/02 Field of Search 96/1 14.8, 1 14.7, 94

References Cited UNITED STATES PATENTS 1/1959 Goldberg et a1. 96/28 2,965,484 12/1960 Tulagin et al 96/98 FOREIGN PATENTS 1,503,373 11/1967 France 96/114.8

761,014 11/1956 GreatBritain OTHER REFERENCES The Electron Microscopy of Photographic Grains. Specimen Preparation Techniques and Applications," Jourml of Applied Physics, Hamm and Comer, 24, pp. 1495- 1513 (1953) Primary Examiner-J. Travis Brown Assistant Examiner-Judson R. Hightower Attorneys-W. H. J. Kline, Bernard D. Wiese and G. L. Hart NEW PIIOTOGRAPIIIC EMULSION WITH A HIGH DEGREE OF COVERING POWER This invention relates to photography and particularly to improvement in photographic silver halide gelatin emulsions.

In its most general aspect, the invention concerns an emulsion that contains, as an adjuvant permitting the increase in the covering power, gelatin that has been treated beforehand with an enzyme.

In British Pat. No. 761,041, a process for preparation of a photographic product has been described in which a gelatino silver halide emulsion is treated by means of an enzyme, the treated emulsion is coated on a support and dried with heat. In this process, the purpose of which is to facilitate the coating of the emulsion, all of the gelatin of the emulsion is hydrolyzed. Nevertheless,it is indicated in this patent that it is preferable to add to the emulsion, before coating, other protective colloids, for example, vinyl copolymers, this being done in order to palliate the low mechanical properties of the hydrolyzed gelatin.

The emulsion and the process according to the invention differ distinctly from those of British Pat. 761,014 and display noticeable advantages, as indicated hereinafter. 1

A photographic emulsion, according to one preferred mode of carrying out the invention, contains a binder comprising a mixture of from approximately 50 parts to 90 parts by volume of gelatin and from approximately parts to 50 parts by volume of a treated gelatin which prior to addition to the emulsion has undergone a careful enzymatic degradation and which, when added to the emulsion, contains practically no active enzyme.

The enzymatic degradation may be followed by a measuring of the viscosity of the gelatin solution. More of less degraded gelatins may be used; however, advantageously used are gelatins, the viscosity of the solution of which has been reduced by degradation to about half that of its initial value.

According to an especially preferred embodiment of the invention, the enzyme-treated gelatin is further treated so that it carries groups resulting from reaction of the treated gelatin with an organic diacid anhydride, such as phthalic anhydride.

Therefore, in accordance with the invention, a process for preparation of a photographic silver halide emulsion comprises the steps of l hydrolyzing a gelatin broth by means of an enzyme solution under controlled conditions of temperature, pH and duration, values of which will be governed by the particular enzyme selected; (2) arresting action of the enzyme when viscosity of the solution has been reduced by enzyme action to a value in the range from about 20 percent to about 80 percent of original viscosity, and (3) adding this hydrolyzed gelatin broth to a gelatino silver halide emulsion, in a proportion from about 10 percent to about 100 percent of the volume of the nonhydrolyzed gelatin initially present in the emulsion.

In preferred embodiments of the invention, the enzyme treatment of the gelatin may be preceded or followed by treatment of the gelatin with an anhydride or an equivalent compound of an organic diacid.

A noticeable advantage obtained by the invention is a marked improvement in covering power of the photographic emulsion containing the treated gelatin. Contrary to what one might expect, the hydrolyzed gelatin, when added to a standard emulsion, in the proportions indicated, does not significantly alter coating and tanning properties of the emulsion and it does not necessitate use of any protective colloid other than gelatin in the emulsion; moreover, conventional coating and drying apparatus may be used. It should be noted that degraded gelatin will not tan but it will absorb a sizable quantity of tanning agent. In those preferred embodiments that comprise treatment of the gelatin with an organic diacid anhydride, such treatment has the effect of blocking certain chains in the polypeptide molecule, and this reduces to considerable degree the absorption of tanning agent for the tanning agent to avoid clinging to a much higher degree to the untreated gelatin.

In the process of the British patent mentioned above, the gelatin is completely hydrolized by enzyme action, so that it requires addition of another protective colloid. Also, it leaves in the emulsion a certain amount of enzyme which may continue to act in the emulsion. In the process of the invention, after treatment to the desired degree by the enzyme, treated action of the enzyme is stopped, and residual enzyme can be eliminated almost entirely by washing before adding the hydrolyzed gelatin to the emulsion. As a result, on the one hand, only a small quantity of enzyme is used (for example, approximately 40 mg. of enzyme per kilogram of dry gelatin) and, on the other hand, there is practically no enzyme in the final emulsion, so that a stable product is obtained.

It must be noted, on the other hand, that gelatin hydrolyzed by means other than an enzyme, for example, by raising or lowering of the does not give the results obtained by the invention. Degradation of the gelatin by the enzyme is a necessary factor but degradation is not sufficient in itself. The enzymatic action is specific: only certain groups of the gelatin are destroyed, or combined with others, depending on the enzyme selected.

For preparation of the hydrolyzed gelatin, one operates in the following manner: A gelatin broth is prepared, for example 500 gm. of a 10 percent broth, to which a quantity of an enzyme solution is added, for example, a l/lOOO aqueous solution containing 2.5 mg. of enyzme and the broth is heated under suitable conditions, governed by the enzyme used. For example, with trypsin, the heating may be done starting from the usual temperature at 75 C. for 10 minutes at a pH of 6. One may operate at a higher pH, for example 8, but then the temperature will have to be lowered and/or the duration of treatment reduced. Besides trypsin, one may use as enzyme, pancreating, papain, and the like. Papain has the characteristic of being inhibited by metallic ions. Pepsin is not suitable for the present invention, as it causes a considerable fog without increasing the covering power.

Stopping of the enzymatic action is obtained by a change of conditions, such as by heating to destroy the enzyme or by modifying the pH to inactivate the enzyme or by introducing inhibitors. The gelatin broth is then washed, in order to remove the enzyme, and is then ready to be added to the emul- SlOn.

For a typical preparation of an emulsion embodying the invention, a quantity of the hydrolyzed gelatin is added to an already made gelatino silver halide photographic emulsion in a proportion amounting to from 10 percent to percent by volume (assuming equal concentrations in the gelatin solutions) with respect to the gelatin already in the emulsion. Quantities below 10 percent and above I00 percent may be used; however, the favorable effects obtained below [0 percent are only weak and addition of a quantity much over I00 percent gives no additional advantages as far as the covering power is concerned and, in general, should be rejected for economical reasons and in order to avoid weakening too much the mechanical properties of the emulsion layer. Considered as percentage by weight of the total gelatin present, then the proportions of treated gelatin mentioned amount to from about 9 percent to about 50 percent by weight. In general, proportions of from 30 percent to 70 percent of gelatin hydrolyzed with enzyme with respect to the other gelatin or other hydrophilic colloid of the emulsion are preferred. Thus. the proportion of hydrolyzed gelatin as part of the total hydrophilic colloid of such an emulsion usually will lie between 25 percent 40 percent by weight.

We have mentioned untreated gelatin as the additional hydrophilic colloid but it will be understood that the invention contemplates use of the treated gelatin for improving covering power of emulsions comprising other suitable emulsion binding agents or gelatin substitutes or other hydrophilic colloids instead of the untreated gelatin used in this specification to describe our most preferred embodiments. Gelatin hydrolyzed by an enzyme may be added to almost any gelatino silver halide photographic emulsion in order to improve its covering power. However, since the larger the size of the grains, the lower the covering power of the developed silver, the process of the invention will be particularly advantageous with coarsegrained emulsions, for example, the highly sensitive ammonia-' broth is heated gradually up to 75 C. for 10 minutes at a pH of 6. At 75 C., trypsin is almost completely destroyed. The broth is cooled then is added to 1,300 9. of a gelatino silver bromoiodide radiographic emulsion, for medical use, containcal emulsions. With the addition of hydrolyzed gelatin, it will 5 ing l.l5 gram atoms of silver and 90 g. of gelatin, before the be possible to increase the covering power for an equal silver chemical ripening. The emulsion is completed in the usual content or, if increased density is not desired, the invention manner and it is coated with various silver contents. permits use of an emulsion with a lower silver halide content The results obtained are given in table I in comparison with to produce the same density. It must be noted, that previous 8 C nt l samp means for improving covering power such as modification of 10 the ratio between gelatin and silver, the use of various adjuvants or the increase of the silver content, have a certain number of inconveniences. For example, they may lead to emulsions that are more fragile to abrasion when humid, or T BL 1 they may increase too much the granulation, or also they may sensimmemc characteristics increase the cost of the emulsion. Test gs/ 3 31 I I n The adding of the treated gelatin may be done at any stage Emulsion i g 21%;: Fog 3,132,. of the emulsion preparation, for example, before or after the L Untreated 1m 0 300 2- I, 0. 04 3. 34 physical and chemical ripening. If the effect on covering Treatedh" 0, 304 3,5 0, m 4.72 power is found to be optimum when the gelatin treated with 3- g------- gg-g 2% 3 8-82 5}? enzyme is added before chemical ripening, still it may be preferable to add it after such ripening in order to obtain an excellent tanning. Usually the effect on the covering power will still be very close to the optimum.

As indicated above, emulsions obtained by the addition to a gelatino silver halide emulsion of a gelatin hydrolyzed with an, The sehsitometrie eharaetelisties are measured from enzyme makes possible the increase of the covering power P exposed fer 1/50 Seeohd in an Eastman sensitomeief, and, since the added quantity of the hydrolyzed gelatin is developed for 3 minutes in a Photographic developer of the small, an emulsion is obtained that has viscosity and susceptifollojvihg composition followed y conventional fixing and bility to tanning that are satisfactory. According to a preferred washmg: embodiment, however, viscosity and susceptibility to tanning may be improved by treating the hydrolyzed gelatin that is Lukewarm 'Q PP' 50C) 750 added to the emulsion with an anhydride or equivalent com 2 pound of an organic diacid. Besides phthalic acid anhydride, 35 Potassium bromide 4 E: which we prefer for this purpose, one may also use, for exam- Cold water suffisiem q y for l liter ple, succinic anhydride and maleic anhydride. As indicated above, this treatment may be ff d b f r or ft the enzy- Sensitivity indicated in Table I and following tables is the matic treatment. Moreover, the gelatins that are added in the Value of 100 8 E), where 5 represents Value of exposul'e course of manufacture of the emulsion, before the physical 0 to obtain dehshy above the fog and pp y" ripening, are often treated beforehand with phthalic anhydride, which imparts to them flocculation characteristics EXAMPLE2 that facilitate the subsequent washing of the formed silver ha- The H of 500 g. of a 10/100 gelatin solution is adjusted to lides- In the case Where hydrolyzed gelatin is added before 10 and the solution is then treated with 2.5 g; of 12.5 percent physical ripening, it will then be advantageous to effect the h h li h d id l i i acetone, i h i dd treatment with such an anhydride, on the one hand, in order to gradually over a period of 30 minutes while keeping pH at [0. facilitate the subsequent washing and, on the other hand, to Th H i h dj to 6 and 25 mg, f() percent trypsin facilitate the tanning However, the twiee'h'eated gelahhs y aqueous solution added. The solution is then heated to 70 C. be introduced a! y Stage Di-manufacture of the emulsion for 10 minutes, the gelatin solution is cooled and is added, be-

Treatmeht of gelatin Whh Phthahe ahhych'ide or with fore chemical ripening, to 1,300 9. of a gelatino silver ec-luwaleht compound is know" and has been described in bromoiodide radiographic emulsion containing 90 g. of gelatin French N 970,317 h and 1.15 gram atoms of silver. The emulsion is then chemical The followlhg a p lhustfale the lhvehhoh by detalled ripened and completed in the usual manner and is coated at reference to Speelfie embodiments lheludlhg our most different thicknesses to give the silver contents shown in table preferred mode of carrying out the invention.

EXAMPLE 1 Sensitometric results are given in table ll with same for a control sample. 500 gm of a 10 percent aqueous broth is treated with 2.5 cc. The sensitometric measurements have been effected in the of 0.1 percent aqueous solution (2.5 mg. of enzyme). The same mannerasin example 1.

TABLE II Sensitometric characteristics After 7-day heating Originally 50% RH and 50 C. Ag/co i- Melting Test tent in Sensi- Sensipoint No. Emulsion mg./dm. tivity Fog tivity v Fog in C 5 Untreated control gelatim 111. 2 294 3, 1 0. 04 305 3. 1 0. O9 53 6 Treated gelatin 104 295 3. 35 0. 02 311 3.3 0.07 48 7 .-d0 80. 4 294 2. 9 0.01 309 3 0, 06 47 NOTE: RH means relative humidity.

3,615,626 I 6 EXAMPLE 3 The film in test No. 12, table IV is found to be especially well suited for use in automatic processing which involves the 700 g. of abroth treated as in example 2 are added, after use of viscous processing solutions; better than the control chemical ripening, to 1,300 g. of a gelatino silver bromoiodide emulsion with gelatin sublayer, and definitely better than the emulsion containing 1.15 gram atoms of silver and 90 g. of 5 emulsion treated y with enzyme gelatin. The emulsion is tanned with cc. of a 1.80 percent The use Ora gelatin treated with an enzyme and whh P mucochloric i aqueous Solution, h coated on a fil ic anhydride makes it possible to obtain the advantages of the pol-L gelatin treated with the enzymes, that is to say, essentially the The control sample is prepared the same manner, except improvement of the covering power while maintaining excelthat the emulsion contains 500 g. of a solution of gm. of 10 lent physical qualities, permitting the use of such films in autocopoly (vinyl alcohol-vinyl acid succinate) such as disclosed matic p s g qu pment without need for a gelatin in US. Pat. No. 3,165,412 issued on Jan. .12, 1965, instead of ubl yer his naturally reduces the cost of making the 700 g. of the broth treated as in example 2. This copolymer is P known addendum for increasing the covering power. This invention has been described in considerable detail Sensitometric results are given in table 111. 15 with particular reference to preferred embodiments thereof TABLE III Sensitometric characteristics 3-min. processing G-min. processing Ag/con- Melting Test tent in Sensi- Sensipoint No. Emulsion mgJdln. tivity 1 Fog tivlty 'y Fog in C. 8 Control sample 119.8 314 3. 3 0.05 324 3. 05 0.08 95 9 Treated gelatin. 117. 2 316 3 0. 04 325 2. 75 0. 11 74 in table [II the Sensitometric characteristics were obtained but it will be understood that variations and modifications can as in example 1 with samples using both 3 minute developbe effected within the spirit and scope of the invention as ment and 6 minute development. described hereinabove and as defined in the appended claims.

We claim:

1. In a photographic silver halide emulsion comprising an EXAMPLE 4 enzyme-treated gelatin as a part of the binder of such emulsion, the improvement wherein from about 9 percent to about 700 gram f3 10 percent gelatin aqueous broth are treated 50 percent Of the total binder present in the emulsion lS a with 2.8 mg. of 0.1 percent trypsin aqueous solution and the hydrolyzed gelatin that has been Partially hydrolyzed y heatbroth is heated gradually for 10 minutes to 70 C. At this temment with enzymes and the enzyme aelion arrested before eram th r i i l t completely d d Af dition of such treated gelatin in the emulsion, the effect of cooling, the pH is adjusted to 10 and the broth is treated with Such i p m t ng n appreciable increase in covering 3.5 g. of 12.5 percent solution of phthalic anhydride in power of the emulsion as compared with an emulsion the same acetone. The phthalic anhydride solution is added gradually to except for such treated gelatinthe hydrolyzed gelatin over a period of 30 minutes, while The p e e a Photographic mf-" flefihed y kee ing the H teady at 10, The luti i l d d i H claim 1 whereln sald enzyme-treated gelatln portlon of the i adjusted t 6, binder has been further treated by reaction with an organic The gelatin broth is then added to 1,300 g. of a gelatino diacid anhydride prior to incorporation of said treated portion silver bromiodide radiographic emulsion containing 1.15 in the emulsionmoles of silver and 90 g. of gelatin. The emulsion has already 3. The improvement in a photographic emulsion defined by undergone the conventional ripenings. claim 2 wherein said acid anhydride is phthalic anhydride.

The emulsion containing the treated gelatin is then tanned 4- h imp o ement in a photographic emulsion defined by by adding 500 mg. of mucochloric acid in the conventional claim 1 wherein said enzyme is trypsin.

manner. The emulsion is then coated on a conventional film 5. The improvement defined by claim 3 wherein the remainsupport. ing portionof said binder is gelatin and said enzyme is trypsin.

Sensitometric results are shown in table IV with same for a 6. A photographic silver halide emulsion comprising an control emulsion that is coated over a subcoat of gelatin on a emulsion binder which comprises as an essential component film support. The sub is not needed for the treated emulsions. thereof from about 9 percent to about 50 percent by weight The control emulsion contains the same amount of the based on the total weight of the binder, of a composition concopolymer used in the control sample of example 3,instead of sisting of treated gelatin that has been at least partially the ,700 g. of the treated gelatin. hydrolyzed by action of enzymes and the enzyme action then TABLE IV Sensitometric characteristics Aglcolltent (2 Processing sides) in Melting point duration Sellsi- Maximum Test No. Emulsion rng./drn. of side lll C. in min. tivity v Fog density 10 Control sample with S.C.G.= 120 100 g g 8 3g 2 ll Treated enzyme, without S.C.G 122 37 40{ 8:22 3.?3 6 323 3.05 0.04 3.63 12.... Treated enzyme plus anhydrlde-phthallc lthout S.C.(:. 82 84 b 331 2 95 0 06 3' 60 :E S.C.G. means sub-layer of gelatin."

The Sensitometric results are obtained in the same manner arrested, prior to incorporation of such composition into the as in example 1. 5 emulsion.

7 7 A photographic silver halide emulsion defined by claim 6 wherein the said enzyme treated gelatin portion of the binder has been further treated with reaction with an organic diacid anhydride prior to incorporation of said treated portion in the emulsion.

8. A photographic silver halide emulsion defined by claim 7 wherein said diacid anhydride is phthalic anhydride.

9. A photographic silver halide emulsion defined by claim 6 wherein said enzyme is trypsin.

10. A photographic silver halide emulsion defined by claim 8 wherein the remaining portion of said binder is gelatin and said enzyme is trypsin.

11. A method for improving covering power of gelatin comprising the steps of 1. partially hydrolyzing gelatin by action of enzymes followed by 2. stopping enzymatic action on the gelatin followed by 3. adding the hydrolyzed gelatin to a photographic silver ha- 12. A method defined by claim 11 further comprising a step either before or after said partially hydrolyzing step and before said adding step, the step of treating the same gelatin by reaction with an organic diacid anhydride.

13. A method defined by claim 12 wherein said diacid anhydride is phthalic anhydride.

14. A method defined by claim 11 wherein said enzyme is trypsin.

15. A method defined by claim 13 wherein the remaining portion of binder for said photographic silver halide emulsion consists of gelatin and said enzyme is trypsin.

16. A photographic recording element comprising a support and c thereon a photographic silver halide emulsion defined by claim 6.

17. A photographic recording element comprising a support and coated thereon a photographic silver halide emulsion defined by claim 7.

18. A photographic recording element comprising a support and coated thereon a photographic silver halide emulsion defined by claim 8.

19. A photographic recording element comprising a support and coated thereon a photographic silver halide emulsion defined by claim 9.

20. A photographic recording element comprising a support and coated thereon a photographic silver halide emulsion defined by claim 10.

mg? UNirED STATES-PATENT OFFICE" CERTIFICATE OF CORRECTION Patent No. 3,615,626 Dated October 26, 1971 Inventor) Claude G. Dostes Jean C. Collange and Guy H. Leverrier It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

On the title page, the first inventor's name "Claude Guy Doste" should read Claude Guy Dostes---;

Column 1, line 10, 'British Pat. No. 761,041" should read British Pat. No. 76l,0l4--;

Column 4 line 3 "l ,300 9." should read 1 ,300 gm.

Column 4 line 50, "l, 300 9. should read -l ,300 gm.

Column 8, line 9, (claim 16) "c" should read ---coated-.

Signed and sealed this 15th day of May 1973.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents 

2. The improvement in a photographic emulsion defined by claim 1 wherein said enzyme-treated gelatin portion of the binder has been further treated by reaction with an organic diacid anhydride prioR to incorporation of said treated portion in the emulsion.
 2. stopping enzymatic action on the gelatin followed by
 3. adding the so hydrolyzed gelatin to a photographic silver halide emulsion.
 3. The improvement in a photographic emulsion defined by claim 2 wherein said acid anhydride is phthalic anhydride.
 4. The improvement in a photographic emulsion defined by claim 1 wherein said enzyme is trypsin.
 5. The improvement defined by claim 3 wherein the remaining portion of said binder is gelatin and said enzyme is trypsin.
 6. A photographic silver halide emulsion comprising an emulsion binder which comprises as an essential component thereof from about 9 percent to about 50 percent, by weight based on the total weight of the binder, of a composition consisting of treated gelatin that has been at least partially hydrolyzed by action of enzymes and the enzyme action then arrested, prior to incorporation of such composition into the emulsion.
 7. A photographic silver halide emulsion defined by claim 6 wherein the said enzyme treated gelatin portion of the binder has been further treated with reaction with an organic diacid anhydride prior to incorporation of said treated portion in the emulsion.
 8. A photographic silver halide emulsion defined by claim 7 wherein said diacid anhydride is phthalic anhydride.
 9. A photographic silver halide emulsion defined by claim 6 wherein said enzyme is trypsin.
 10. A photographic silver halide emulsion defined by claim 8 wherein the remaining portion of said binder is gelatin and said enzyme is trypsin.
 11. A method for improving covering power of gelatin comprising the steps of
 12. A method defined by claim 11 further comprising a step either before or after said partially hydrolyzing step and before said adding step, the step of treating the same gelatin by reaction with an organic diacid anhydride.
 13. A method defined by claim 12 wherein said diacid anhydride is phthalic anhydride.
 14. A method defined by claim 11 wherein said enzyme is trypsin.
 15. A method defined by claim 13 wherein the remaining portion of binder for said photographic silver halide emulsion consists of gelatin and said enzyme is trypsin.
 16. A photographic recording element comprising a support and coated thereon a photographic silver halide emulsion defined by claim
 6. 17. A photographic recording element comprising a support and coated thereon a photographic silver halide emulsion defined by claim
 7. 18. A photographic recording element comprising a support and coated thereon a photographic silver halide emulsion defined by claim
 8. 19. A photographic recording element comprising a support and coated thereon a photographic silver halide emulsion defined by claim
 9. 20. A photographic recording element comprising a support and coated thereon a photographic silver halide emulsion defined by claim
 10. 